Scientists believe climate change could be behind the mystery of Lough Neagh's disappearing ducks.
More than 100,000 water birds used to flock to the huge lough around 20 years ago to overwinter, and now that figure has plummeted to 50,000 or 60,000 - a faster decline than elsewhere in the UK and Europe.
Ian Enlander, head of the ornithology team on site designations with the Environment and Heritage Service, will reveal the shock drop in numbers at a conference this morning which unveils the latest research carried out by the government body.
Environment Minister Arlene Foster will host the conference at the Waterfront Hall.
The conference uncovers the world beneath our waves revealed by scientists creating a 3D model of the seabed, the threat to Northern Ireland's bees, the news that the Irish hare may be a distinct species and the discovery of more than 100 rare invertebrates, some new to Ulster.
Delegates heard that Lough Neagh used to be one of the top 10 wetland sites in the UK for wintering birds but has declined to around 20th.
Mr Enlander said reviews of bird ringing programmes suggest that whereas wildfowl once migrated from Iceland, the Baltic states and Europe to overwinter in Lough Neagh, many are now staying put.
Some reports favour climate change as the main cause of this decline, while others suggest diminishing habitat quality in Lough Neagh could be to blame.
"The data shows that in places like the Baltic states winters are milder than they were 30 to 50 years ago. If the birds believe they can have a comfortable winter near their breeding grounds, then why fly that extra distance?" Mr Enlander asked.
"We have found significant decreases in the distances that the average bird is flying towards its wintering grounds, and more detailed work by other groups on waders such as curlew and oystercatchers finds that they're moving north."
However, Mr Enlander stressed that EHS needs to investigate whether other factors could be at play - that the ducks have disappeared faster than elsewhere suggests something specific to Lough Neagh is affecting them.
"There is a tendency to blame it all on climate change and wash your hands and say there is nothing we can do about it - and that is a very poor response to make."
He said more work is planned to determine what local factors could be involved.
"My concern is whether changes in water quality have fed down the food chain and impacted on the Lough Neagh flies they feed on.
"We know that Lough Neagh is not as clean as it should be, but we can't point at any other changes that tie into the big changes that we've seen with the birds," he said.